Along with the miniaturization of electronic parts, spring members used for the electronic parts are more and more laminated, and therefore it is necessary to further improve their strength and bending workability. Beryllium copper typified by C1720 is known as a copper alloy material for electronic parts provided with both high strength and bending workability. However, with consideration for recent environmental issues, there is a trend toward avoiding the use of alloy materials containing Be.
Thus, Cu—Ni—Sn-based alloys are becoming a focus of attention as copper alloys taking the place of beryllium copper. For this Cu—Ni—Sn-based alloy, a modulation structure is formed through aging treatment, and as a result, the Cu—Ni—Sn-based alloy is known to be an alloy that provides high strength. Studies have been carried out so far on its composition, working, heat treatment, elements added and structure, and it has been reported that the Cu—Ni—Sn-based alloy can further improve strength and bending workability.
As a conventional Cu—Ni—Sn-based alloy, an alloy is disclosed which contains, as principal ingredients, 3 to 12 mass % of Ni, 3 to 9 mass % of Sn and Cu as the remainder in order to improve bending workability, and is subjected to (1) heat treatment at 730 to 770° C. for 1 to 3 minutes prior to final finishing of the alloy, (2) rapid cooling quenching, (3) 55 to 70% cold working, and (4) heat treatment at 400 to 500° C. for less than 1 to 3 minutes (e.g., see Patent Literature 1).
Moreover, as another conventional Cu—Ni—Sn-based alloy, an alloy is disclosed which contains, as principal ingredients, 5 to 20 mass % of Ni, 5 to 10 mass % of Sn and Cu as the remainder and in which a ratio of an average diameter x of crystal grains in a plate width direction to an average diameter y parallel to a rolling direction (y/x) is set to 1.2 to 12, and 0<x≤15 and the number of second-phase grains having a major axis of 0.1 μm or more observed by a cross section speculum is assumed to be 1.0×105/mm2 or less (e.g., see Patent Literature 2).